multi-higgs doublet model can it account for l^+l^-gammagamma eventsnew

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1、DO-TH/92-24December1992Multi-HiggsDoubletModel:CanItAccountforl+l−γγEvents?G.Cvetiˇc,M.NowakowskiandYue-LiangWuInst.f¨urPhysik,Universit¨atDortmund,4600Dortmund50,GermanyABSTRACTMotivatedbyrecentexperimentsatLEP(Z→l+l−γγ,withM≃59GeV),weγγarXiv:hep-ph/9

2、302262v116Feb1993examinethepossibilitythatsucheventsareexplainedbyaBjorkenprocesswitharesonantHiggs(Mho≃59GeV)decayingtoγγ.OurmodelisanN-doublet-HiggsmodelwithoutCP-violation.Underthesimplifyingassumptionthat(N−k)doublets(k≥1)decouplefromthefermionsect

3、or,wecouldexplaintheobservedeventsif:i)(N−1)≥2andii)themassesofthecorresponding(N−1)neutralscalarsareeithercompletelyoralmostdegenerate,i.e.thedecayZ→l+l−γγproceedsnowviaseveraloverlappingresonances.1Recently,theL3CollaborationhasfoundfoureventsZ→l+l−γ

4、γwiththeinvariantmassofthephotonpairsMγγ≃59GeV[1].ThetotalnumberofthecorrespondinganalyzedZ-decaysisN=1.6×106[2](upuntilmid-November1992).totInthisletter,weinvestigatethepossibilitythatthisprocessisrealizedviathe∗o∗+−oBjorkenprocessZ→Zh,whereZ→llandh→γ

5、γ(Mho≃59GeV),withinthesimplestpossibleextensionsoftheminimalstandardmodel(SM)-thosewithNscalarisodoublets(N≥2).Theobserveddecayscan’tbeexplainedwithintheminimalSM(N=1),amongotherthingsbecausethebranchingratiosΓ(ho→γγ)/Γ(ho→all)≪1(e.g.,thedecaysho→¯bbwo

6、uldbemuchmorefrequentthanho→γγ).Thereare,ingeneral,threeproblemswhenonetriestoexplainthesehighphotonmasseventsbyaBjorkenprocess.Eachoftheseproblemsisconnectedtooneoftheverticesinthedecaydiagram.1.ThefirstproblemisthedeficitoftheZ→ννγγ¯andZ→qqγγ¯events,re

7、lativetoZ→l+l−γγevents.Sincetheexperimentalresultsmightbetootentativetodrawdefiniteconclusionsonthispoint,wewillnotdiscussithere.2.ThebranchingratioB(ho→γγ)shouldbeoftheorderone.ThisisexcludedintheminimalSM,butcouldbearrangedinamulti-doublet-Higgsmodel(

8、seebelow).3.Thethirdproblemconcernstheon-shellproductionrateforZ→Z∗ho→l+l−ho.InSM,onepredicts1.3sucheventsifMho≃59GeVandthetotalnumberofZ-decaysis1.6×106.Thiswouldmakeitdifficulttoreconciletheobservedfoureventswiththetheory,evenwhenB(ho→γ